Control strategies for internal combustion engines have evolved from purely electromechanical strategies to increasingly more complex electronic or computer controlled strategies. Spark-ignited internal combustion engines have traditionally used air flow as the primary control parameter, controlled by a mechanical linkage between a throttle valve and an accelerator pedal. Fuel quantity and ignition timing, originally mechanically controlled, were migrated to electronic control to improve fuel economy, emissions, and overall engine performance. Electronic throttle control systems have been developed to further improve the authority of the engine controller resulting in even better engine performance.
Electronic throttle control replaces the traditional mechanical linkage between the accelerator pedal and the throttle valve with an "electronic" linkage through the engine or powertrain controller. Because of this electrical or electronic linkage, this type of strategy is often referred to as a "drive by wire" system. A sensor is used to determine the position of the accelerator pedal which is input to the controller. The controller determines the required air flow and sends a signal to a servo motor which controls the opening of the throttle valve. Control strategies which imitate the mechanical throttle system by controlling the opening of the throttle valve based primarily on the position of the accelerator pedal position are often referred to as pedal follower systems. However, the ability of the controller to adjust the throttle valve position independently of the accelerator pedal position offers a number of potential advantages in terms of emissions, fuel economy, and overall performance.
An engine control strategy typically has a number of operating modes, such as idle, cruise control, engine speed limiting, vehicle speed limiting, dashpot, normal driving, etc. The various control modes may or may not use the same or similar primary control parameters. Furthermore, modes of operation often use different control strategies, which may include open-loop and/or closed loop feedback/feedforward control strategies. Likewise, different strategies may utilize proportional, integral, and/or derivative control with control parameters tuned to particular applications or operating conditions.
To provide optimal driving comfort and robust control of the engine under varying conditions, it is desirable to provide smooth transitions between control modes. In particular, it is desirable to provide smooth or seamless transitions between idle control mode, where the accelerator pedal is not depressed, and a normal driving mode where the accelerator pedal is depressed.